(Invited) Development of High Mobility Polymer Semiconductors for p-Channel, n-Channel, and Ambipolar Thin Film Transistors

Polymer semiconductors are enabling materials for a wide range of printed electronics. As channel semiconductors for organic thin film transistors (OTFTs), charge carrier mobility on par with that of amorphous silicon (~0.5 cm²V^-1s^-1) or higher is required for many applications. The development of polymer semiconductors with high mobility and good ambient stability has been a great challenge. To improve the charge carrier transport, a combination of donor and acceptor units in an alternating fashion in the polymer backbone has been recently found very effective since the intermolecular donor-acceptor attraction can shorten the interchain distance. By utilizing this strategy, we have developed a number of donor-acceptor polymers semiconductors with very high mobility. One particular class of such polymers are based on a diketopyrrolopyrrole (DPP) acceptor building block. By carefully choosing the electron donor blocks, we have successfully developed p-type polymers with high mobility up to 6.9 cm²V^-1s^-1 and amibipolar polymers with balanced electron and hole mobility of 6.30 cm²V^-1s^-1 and 2.78 cm²V-1s^-1, respectively. By using a ultra-thin layer (~2-5 nm) of polyethylenimine (PEI) to lower the work function of the source and drain contacts, we were able to block the hole injection and successfully transform ambipolar and even p-type transistors unipolar n-type transistors. This general approach to converting the transistor polarity broadens the scope of available polymer semiconductors for constructing n-channel transistors.

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